Tolong bantu no 3,4,6

[tex]3) \: u3 = a + 2b = 17\\ \: \: \: \: \: u5 = a + 4b = 31 \\2b = 14. \: \: b = 7. \: \: a = 3 \\ u20 = a + 19b = 3 + 19 \times 7 = 136 \\ 4) \: u3 = a + 2b = 18 \\ \: \: u7 = a + 6b = 38 \\ 4b = 20. \: \: b = 5. \: \: a = 7 \\u24 = a + 23b = 7 + 23 \times 5 = 122 \\ s24 = \frac{24}{2} (7 + 122) = 12(129) = 1548 \\ 6) \: r = 3 \\ s5 = \frac{a( {r}^{n} - 1) }{r - 1} = \frac{2( {3}^{5} - 1)}{2} = 242[/tex]